1. Field of the Invention
The present invention relates to a tensioner for a wrapping connector transmission device for an internal combustion engine, in which it is automatically arranged that an endless transmission member as a wrapping connector stretched between a driving wheel and a driven wheel supported on the engine body is adapted to run under a constant tension at all times.
2. Description of the Prior Art
It has been heretofore known in a conventional combustion engine to stretch and wrap an endless transmission member between a driving wheel and a driven wheel and connect an automatic adjuster to a tensioner body which is pressed against the transmission member thereby to allow the transmission member to run under a constant tension at all times (Japanese Utility Model Application Laid-Open No. 202,039/82).
It has also been well known, in an internal combustion engine of the type having a crank shaft connected with a driving wheel and a valve operating cam shaft connected with a driven wheel and further having an endless transmission member stretched between the driving and driven wheels, to urge a tension pulley of a tensioner, supported on the engine body through an oscillating lever, into pressure contact by means of an automatic adjuster against the loosening side of the endless transmission member thereby permitting the transmission member to run under a given tension (Japanese Patent Application Laid-Open No. 208,251/84).
However, conventional tensioners of the mentioned type suffer from such problems that the tension pulley is caused to repeat its oscillating motion along with the oscillating lever by variation in tension of the endless transmission member, and that the pulley is subjected to vibrations of the transmission member to displace in its axial direction showing a tendency of floating up relative to the engine body, and such tendency increases particularly when the engine operates at a high speed.
In addition, in such a tensioner, reaction from the transmission member acts on a pivot portion of the oscillating lever and a supporting portion of the automatic adjuster and, therefore, it is necessary for assuring a predetermined tension to the transmission member efficiently, to increase the rigidity of the pivot portion of the oscillating lever and supporting portion of the automatic adjuster.
Furthermore, when an automatic adjuster for the tensioner is constructed of a hydraulically operated type, a closed loop type and an externally oil replenished type are known to be used. The closed loop type is advantageous in that a passage for replenishing oil from the outside is not required but involves a problem in reliability because of deterioration and leakage of oil sealed in the adjuster. On the other hand, the externally oil replenished type is free of the problem noted above but poses a separate problem in that a passage to replenish the adjuster with oil from the outside is required, which complicates the construction, resulting in a higher cost.
Moreover, if the automatic adjuster is designed to be a forced oil replenishing type, pressure oil is always forcibly fed thereto to make the operation of the adjuster reliable. However, when the engine is out of operation, oil supply to the automatic adjuster is stopped to cause a drop in oil pressure in the adjuster. As a result, when the engine operation is restarted, the operation of the automatic adjuster is delayed in time causing loosening of the transmission member temporarily. This sometimes leads to a jump between the meshing teeth of the transmission member and the driving wheel. If an attempt is made to increase an adjusting allowance of the automatic adjuster in order to avoid a problem, a further problem may arise to inevitably make the automatic adjuster large-sized which increases the cost.
In addition to overcoming the above disadvantages of the prior art, it is required to design a tensioner of the above type in such a manner that it can be easily mounted on an engine body, the whole operation stroke of an automatic adjuster provided on the tensioner can be effectively utilized to increase the adjusting allowance of a transmission member, the work to adjust the stroke can be conducted easily and the automatic adjuster can be made compact, and that in the case where the automatic adjuster is constructed of a hydraulically operated type, any useless stroke can be eliminated from the adjuster and oil ports formed at relative movable parts in the adjuster can be made as small as possible.
Furthermore, it is desired that the space occupied by the whole wrapping connector transmission device not be so increased even with the arrangement of the aforesaid tensioner, the wrapping angle of the transmission member with respect to the driving and driven wheels be increased, and the load applied to their meshing teeth be minimized to enhance the transmission efficiency, thus prolonging the service life of the transmission member.